How to Think Critically II: Salience

“Just another day in the city. A sidewalk grate, the kind that millions of feet trod upon every day, gives way, sending a woman tumbling into the hole and landing her in the hospital. Downtown, a 15-foot pipe falls off a 40-story skyscraper, crashing through a firehouse nearby, injuring two.

In densely packed Manhattan, with so many taxis speeding down the street, so many subways to trip and fall in front of, and of course so many rapes, robberies and murders to contend with, the whole place can seem like a stage set for ‘Fear Factor.'”

During my morning commute the other day, I caught this headline in a daily newspaper. I have no doubt that as a result of this fear-mongering story, millions of people will steer clear of walking on sidewalk grates for a while, “just to be safe”. How many of those same people will take extra care to look both ways before stepping off a curb? After all, falls through sidewalk grates have killed no people that I am aware of, and have now injured a total of one. By contrast, 200 people are killed every year in New York City by cars.

This fallacy is called the availability heuristic: if an outcome is more accessible cognitively, because it is more easily brought to mind, people will tend to view it as more likely. As security professional Bruce Schneier writes, people consistently underestimate the risk posed by common, everyday events, while overestimating the risk caused by rare, spectacular events. In other words:

Novelty plus dread equals overreaction.

…I tell people that if it’s in the news, don’t worry about it. The very definition of “news” is “something that hardly ever happens.” It’s when something isn’t in the news, when it’s so common that it’s no longer news — car crashes, domestic violence — that you should start worrying.

Schneier gives many more pertinent examples. Shark attacks seem more spectacular and frightening than dog attacks, even though far more people are killed each year by dogs than by sharks. Far more people have phobias about flying than driving, even though mile for mile, driving is a much riskier way to travel. We fear being assaulted or raped by strangers, when relatives and friends of the victim are far more likely to be the perpetrators of such an assault. Terrorist attacks like September 11 so terrify us that we are willing to spend billions of dollars on “homeland security” in municipalities across the country; meanwhile, car crashes kill many times more people each year than terrorists ever have. We react with horror to tragedies like the Virginia Tech shooting spree and agonize over how to prevent such incidents in the future, when far more people are killed each year in mundane domestic violence. Spending money to protect ourselves against common threats, which are both more preventable and more often overlooked precisely because they are common, would pay greater dividends than spending the same money to protect ourselves against extremely rare and improbable disasters.

The availability heuristic plays an important role in religion as well. Since billions of people pray billions of prayers per day, it is statistically inevitable that in some cases, the outcome prayed for will occur simply by chance. When this happens, believers seize on these events and promote them far and wide as answers to prayer. On the other hand, the far greater number of occasions when prayers do not come true are less cognitively available, and are therefore ignored and forgotten. This combination of counting the hits and forgetting the misses makes it seem, to people who do not understand statistics, as if prayer is highly effective. A similar fallacy can be seen in faith healers, who endlessly recount the few stories of people who recovered naturally after being “healed” and dismiss the far larger number of people who did not.

In the last installment of this series, I wrote about extraordinary claims and under what circumstances we should believe or disbelieve them. But the important corollary is that, even when extraordinary claims are true, we should not let them unduly shape our thinking. They still represent an exception, not the norm. Understanding this would keep many people from accepting claims born of superstitious fear.